In this proposal we will employ loose ligation of the sciatic nerve as a model to further our understanding of the mechanisms underlying the pathophysiology of neuropathic pain, a most-puzzling and treatment-resistant type of chronic pain. The overall goal is to determine whether sciatic ligation in rats (as a form of persistent nociception) produces plastic changes in spinal dorsal horn neuronal function that contribute to the observation of thermal hyperalgesia (as an indicator of neuropathic pain). In the first part of this proposal we will examine whether long-term potentiation (LTP) and long-term depression (LTD), as electrophysiological correlates of synaptic plasticity, can be recorded in the superficial spinal dorsal horn of control, sham-operated or ligated rats in vivo. We will monitor extracellular field potentials that are evoked by high-frequency or low-frequency repetitive stimulation of primary afferent fibers, and determine whether synaptic activity and function are modified over the course of several hours. We are especially interested in establishing whether any observed enhancement or diminution in afferent-evoked synaptic function is a normal feature of dorsal horn neuronal activity, or is specifically observed only after sciatic ligation. In the second part of this proposal we are interested in establishing the possible involvement of protein kinase C (PKC) as a critical, if not crucial, biochemical mediator of any sciatic ligation-induced plasticity in the rat spinal dorsal hoary. We will employ biochemical assays to assess whether sciatic ligation modifies the distribution of total PKC activity, and the quantity of its pII (beta-2), y (gamma) and :, (zeta) isozymes in the cytosolic and crude P-2 membrane subcellular fractions of the spinal dorsal horn of control, sham-operated or ligated rats. We will also use immunocytochemical procedures to visualize any injury-induced changes in the pattern of immunocytochemical staining of the PKC ,BII, y, and (, isozymes in the spinal dorsal horn of control, sham-operated or ligated rats. We hope that the studies in this proposal will yield critical information about the processes underlying neuropathic pain, as well as about potential approaches to more effective clinical treatments.